Despite the popularity of the name aurantiacum for North American Leccinum collections, current morphological and molecular data do not support the idea that Leccinum aurantiacum occurs in North America:

Leccinum aurantiacum is probably a European species, and no records are known from North America. The descriptions of L. aurantiacum in North American literature represent a mixture between a L. vulpinum-like, conifer associated taxon and North American species that are associated with broad-leaved trees, such as L. insigne, and L. brunneum.

den Bakker & Noordeloos, 2005

As it is now defined, Leccinum aurantiacum is a mycorrhizal "generalist," associating with hosts ranging from Fagus and Quercus to Betula and Populus; it is the "one major exception" to high host specificity in the genus (den Bakker et al., 2004b; the paper did not consider species like Leccinum chromapes and Leccinum subglabripes in section Luteoscabra, which may also be generalists). However, Leccinum aurantiacum does not associate with conifers--and this idea, combined with morphological analysis, places many North American "Leccinum aurantiacum" collections in the vicinity of the conifer-loving Leccinum vulpinum.

Morphologically, Leccinum aurantiacum can be separated from similar species (in Europe, at least) on the basis of the "brownish-reddish stipital ornamentation that is already reddish in young fruit-bodies," the red to reddish brown cap, the presence of overhanging flaps, and the reddish brown (in KOH) caulocystidia (den Bakker & Noordeloos, 2005). It is worth pointing out that the original description of Boletus aurantiacus (Bulliard, 1780) was accompanied by a beautiful color illustration clearly depicting reddish brown, rather than black, scabers. To get an idea of what contemporary European researchers have in mind for the reddish brown scaber color in Leccinum aurantiacum, see these photos in the online Leccinum treatment of den Bakker & Noordeloos (2007). Then compare the photo to color illustrations in your North American field guide's treatment of Leccinum aurantiacum. In my library, all the illustrations but one show black, rather than reddish brown, scabers--and close inspection of most of the photos also reveals conifer debris in the vicinity of the mushrooms. One exception is the photo in Phillips (1991), which features a North American aurantiacum-like collection with reddish brown, rather than black, scabers. The following field guide illustrations appear to possibly represent Leccinum vulpinum:

At this point I am not able to formulate a hypothesis regarding where, exactly, Leccinum aurantiacum sensu Smith, Thiers & Watling belongs--but I am also not yet willing to accept the idea put forth by den Bakker & Noordeloos (2005) that "Leccinum aurantiacum is probably a European species, and no records are known from North America." Though they are correct that much of what is called "Leccinum aurantiacum" on this continent probably belongs in Leccinum vulpinum, we do appear to have an aurantiacum-like taxon with reddish brown scabers, growing under Populus and Betula. When Smith & Thiers (1971) write that "in L. aurantiacum it is not uncommon to find basidiocarps with the stipe nearly white when half expanded and with the ornamentation becoming orange-tan or more reddish before finally going to black," I suspect they are combining their many observations of aurantiacum-like collections and superimposing, at least in part, an artificial experiential continuum--especially since Smith & Thiers were at odds with Singer on a concept for Leccinum and were somewhat stubbornly insisting on blackening scabers for the genus (see Smith & Thiers, 1968) despite describing taxa with pale scabers (as pointed out by Singer, 1986). In short, I am not convinced that all of the reddish-brown scabers in North America darken to black. And while den Bakker & Noordeloos cite plenty of material to support reliable conclusions about European species, their experience with North American specimens is minimal and may easily be insufficient to declare that Leccinum aurantiacum, which their own previous publication (2004b) argues is a highly facultative generalist, does not occur here.

The European Leccinum crocipodium is mycorrhizal with oaks or hornbeam, and is well supported (see den Bakker & Noordeloos, 2005). Separation from North America's Leccinum rugosiceps is supported by preliminary molecular evidence (Binder & Hibbet, 2004; den Bakker & Noordeloos, 2005) and by morphology: Leccinum crocipodium has a bright yellow pore surface when young, a yellowish stem that is habitually (though not always) swollen in the midportion, and scabers that are frequently arranged in a pattern of lines or ridges, suggestive of a wide-meshed reticulum.

However, the presence of Leccinum crocipodium in North America is certainly debatable. Very few North American records for the taxon exist, and several of the existing records are dubious. (I have not collected the species, nor have I examined material collected by others.) Only seven records for Leccinum crocipodium can be found in online herbaria. In NY, Halling 7216 (from Costa Rica) is catalogued as Leccinum crocipodium--but this collection is cited in Halling & Mueller (2003) as a collection of Leccinum neotropicalis. No records for Leccinum crocipodium occur in TENN or OSU. BPI holds one collection (McKnight 14147, from Virginia in 1974). MICH holds five collections: two from Europe; an early Smith collection (AHS 7485) from Tennessee in 1937, not cited by Smith in his later publications treating the taxon (1967, 1971); and two made by Guravich (803 and 857) in Mississippi in 1976. One of the Guravich collections (it is not entirely clear which) is featured in a photograph of Leccinum crocipodium in Weber & Smith's 1985 Field Guide to Southern Mushrooms (plate 51, page 82); this photo is also used in Bessette, Roody & Bessette (2000, plate Leccinum nigrescens [A], p. 327). I have examined Weber's notes in MICH for "Guravich 803 also 857," which indicate some struggle with identification (several taxon names have been crossed out and amended), though her final conclusion appears to be "crocipodium ss. late European authors (not Boletes of Mich)." The Guravich photo does make a fairly good match for the European Leccinum crocipodium, and Weber's notes on the exsiccata also describe a plausible match. John Plischke's photo (above) also makes a good match for Leccinum crocipodium; it represents an unvouchered Ohio collection from a club foray (the mushrooms were repositioned for the photo, and data for the collection's ecology is not available). The European species is well represented by online photographs that appear to correspond with the 2005 description by den Bakker & Noordeloos (examples include Snowarski, 2003; J.-J. Wuilbaut, 2000; and AMPB, n.d.), and also appear to correspond with the Guravich and Plischke photos.

"Leccinum crocipodium" sensu Smith, Thiers & Watling (1967) and sensu Smith & Thiers (1971) may be different. The authors described Leccinum crocipodium in North America on the basis of a sole collection from an Ypsilanti, Michigan, golf course (AHS 64289), and were careful to note that Leccinum crocipodium was "apparently very rare in North America" and that their collection featured differences from European collections. In the course of identifying the Guravich collections, Weber did not feel that the 1971 Smith & Thiers description corresponded to the Mississippi material or to European descriptions of Leccinum crocipodium, but her decision appears to be based primarily on spore dimensions; she measured "12.0-13.5 (15) X 5-6.5 µm" for the Mississippi collections and wrote "spores small for crocipodium - American variant" in her notes. In describing the Ypsilanti collection, Smith, Thiers & Watling (1967) noted:

Our material differs slightly from descriptions of European collections in having a more permanent scarlet to dull red stipe-base, the surface of the stipe being more olive-buff than yellow when fresh, and in the lack of yellow in the fresh tubes. The latter is the more significant difference but on drying the tubes of the American specimens became yellow so the apparent differences are not given taxonomic emphasis at this time.

These words are not repeated in the more readily available 1971 publication (though the morphological description is reiterated word for word) and are worthy of attention, since they document some hesitation on the part of the authors. Widespread use of The Boletes of Michigan has probably led to many "Leccinum crocipodium" identifications based solely on proximity to Leccinum rugosiceps and width of spores, since the 1971 key to section Luteoscabra points immediately to Leccinum crocipodium if spores measure "6-8 µ in diameter." The Ypsilanti collection does not appear in the online Leccinum records at MICH; either it is in another herbarium (though not NY, BPI, TENN, or OSU) or there is a labeling problem.

Leccinum neotropicalis Halling (1999), well represented by multiple collections under various oaks in Costa Rica, is very similar; it has a bright yellow pore surface and a yellowish stem that is "equal to clavate to subclavate, sometimes with a tapered and pointed base." However, it differs from Leccinum crocipodium in its darker pileus colors, non-staining context, and clavate to lageniform (rather than lageniform to fusoid) caulocystidia.

Molecular Data: Four partial sequences have been deposited in GenBank with the label Leccinum crocipodium. One deposit does not document a collection location; the others are from Belgium, France, and the Netherlands. Several of these sequences have been aligned in recent papers, including Binder & Besl (2000), den Bakker et al. (2004a, 2004b), Binder & Hibbet (2004), and den Bakker & Noordeloos (2005).

Although Dick & Snell listed "white spruce and yellow birch" in "Nova Scotia and Michigan" for habitat and range in their later (1970) publication, the yellow birch and Michigan references should be discounted. Careful reading of four publications that came on one another's heels (Dick & Snell, 1965; Smith Thiers & Watling, 1967; Snell & Dick, 1970; and Smith & Thiers, 1971) reveals that Smith & Thiers thought they had a Michigan collection of Leccinum flavostipitatum, made under yellow birch (AHS 66637, represented by a single mushroom)--but changed their minds after examining Dick & Snell's type collection, since AHS 66637 had a stem that was not yellow in the dried state, as well as tissues that reacted differently to Melzer's and habitat under birch (see Smith, Thiers & Watling, 1967). Dick and Snell apparently did not receive the news that the Michigan collection was not a match for Leccinum flavostipitatum before the 1970 manuscript was in press; Smith & Thiers (1971) then included the taxon in their treatment of Michigan boletes, perhaps to provide a bit of cover for Snell & Dick, saying: "on several occasions we thought we had found it here in Michigan. An examination of the type proved this to be erroneous, but we expect it will eventually turn up in our area."

This taxon was described by Smith, Thiers & Watling in 1967, on the basis of a collection made "under Carpinus caroliniana" by Smith (AHS 73252) in 1966. Although the species had "been found rarely in Michigan since the 1930 decade," the 1966 type collection was "the best one made to date," containing "all stages of development and enough material . . . to assure the constancy of the characters" (1967).

Morphologically, Leccinum luteum has a yellow cap, a whitish pore surface when young, a stem surface with "sparse fine blackish points and squamules," a pileipellis disposed as a trichoderm with inflated terminal elements, and long, fusoid-ventricose caulocystidia that have "a proliferated neck" and are "hyaline to bister" in KOH.

Figure 1 represents Leccinum luteum collections found in online herbaria. Though few collections have been made, Carpinus is fairly clearly indicated; records that do not specify Carpinus do not necessarily exclude it once the tree's tendency to grow as a scattered understory tree is recalled. No sequences labeled Leccinum luteum have been deposited in GenBank.

Whether or not the characters defining Leccinum luteum sufficiently separate it from Leccinum pseudoscabrum is debatable. The Carpinus ecology and the trichoderm with inflated terminal elements, shared by Leccinum pseudoscabrum, might trump the other characters--many of which might be superficial. The yellow cap seems distinct from the gray-brown cap of Leccinum pseudoscabrum, but other species of Leccinum (for example, Leccinum rugosiceps) sometimes demonstrate both yellow and brown caps--and Lannoy & Estades (1995; plate 42) illustrate a yellowish form of Leccinum pseudoscabrum ("Leccinum carpini f. isabellinum") in Europe, with a cap color very close to that of Leccinum luteum. The proliferated caulocystidia seem distinctive, but in the European context den Bakker & Noordeloos (2005) document the feature on other taxa (see Figure 14, for Leccinum schistophilum, and Figure 8, for Leccinum vulpinum) but do not even describe it, placing emphasis instead on the shapes and KOH staining reactions of the caulocystidia.

AHS 73252 (Type, in MICH)Courtsey of the University of Michigan Press and Herbarium

Leccinum ponderosum was described by Smith, Thiers & Watling (1966) from Oregon, under "Pinus ponderosa and P. lambertina," with AHS 55718 (in MICH) cited as the type collection. The authors described it as "the monster of all the large western species of Leccinum," with a cap 10-30 cm across. Leccinum ponderosum parallels the contemporary concept of Leccinum vulpinum in its association with conifers, red cap, overhanging marginal flaps, dark scabers, and bluing stem base. Aside from its large size, morphological differences between it and Leccinum vulpinum are potentially negligible: the stem base blues enthusiastically; the scabers are "avellaneous to fuscous" in the fresh state, but "near 'snuff brown'" in exsiccata; the sliced context does not stain "appreciably," though there are "a few gray streaks" on the sliced surfaces of exsiccata; the spores are slightly longer than those cited by den Bakker & Noordeloos (2005) for Leccinum vulpinum; the hymenial cystidia are brown or ochraceous in KOH, rather than reddish brown; and the caulocystidia are "smoky ochraceous" rather than brownish. Aside from the type collection, MICH holds three collections labeled Leccinum ponderosum; of these, two are not annotated and the third lists "Pinus" as the associated tree. One well documented collection labeled Leccinum ponderosum in OSU lists "Tsuga mertensiana, Abies amabilis, Pinus contorta, Picea engelmannii, Vaccinium membranaceum, Vaccinium scoparium" (four conifers and two bushes in the Ericales) under habitat. BPI holds one collection of Leccinum ponderosum; it appears to be a combination of two Smith collections (AHS 15897 and AHS 15935) from Idaho in 1941, made under spruce, coming to BPI via the private herbarium of Snell. No collections are held in NY or TENN, and no sequences labeled Leccinum ponderosum have been deposited in GenBank.

Described by Singer & Williams (1992), Leccinum roseoscabrum certainly appears morphologically distinct from close relatives on the basis of the characters emphasized in the key (see couplet 9)--and possibly by its host preference. I do not find microscopic characters in the species description (which is quite thorough) that would help to separate this taxon from Leccinum crocipodium or Leccinum rugosiceps. Microscopic features (spores, basidium, hymenial cystidia, pileipellis elements, and caulocystidia) are illustrated in the authoring publication; a photograph of mushrooms in the fresh state, taken by Williams, can be found in Bessette, Roody & Bessette (2002, p. 328; plate "Leccinum roseoscabrum A"). Singer & Williams cite two collections in F as the type and holotype; I know of no other records of this taxon. No sequences labeled Leccinum roseoscabrum have been deposited in GenBank, and no papers that I am aware of have aligned its DNA. Hopefully the inclusion of Leccinum roseoscabrum in the popular field guide by Bessette, Roody & Bessette will lead to further collections, identifications, and documentation (especially of precise host preferences).

I believe that Leccinum rubropunctum may be a distinct morphological species, separated from Leccinum longicurvipes on the basis of the characters used in the key (see couplet 8). Roy Halling's concept of the species, illustrated in this photo in NY online records, probably represents Peck's mushroom. However, I am treating the taxon as "uncertain" because we have few reliable descriptions of the mushroom's macromorphology other than Peck's original account: pileus "reddish-brown, flesh yellowish, unchangeable; tubes bright golden yellow, stipe yellow, punctate with reddish dots or squamules" (quoted in Both, 1993). Other accounts come from authors (Coker & Beers, 1943; Singer, 1947; Snell & Dick, 1970) who thought rubropunctum and longicurvipes were synonyms, and may represent mixed data. Semi-technical field guide descriptions (Smith, Smith & Weber, 1981; Bessette, Roody & Bessette, 2000) are not thorough and should not be relied on. Smith & Thiers (1971, p. 315) studied the type collection of Boletus rubropunctus and recorded micromorphology thoroughly, but did not describe any of their own collections. One of Smith's collections in MICH (AHS 10315) is labeled Boletus rubropunctus, but should be viewed as suspect since it was made on the same day, in the same location as the type collection of Boletus longicurvipes (AHS 10320). One Thiers collection in MICH (HDT 7097) from Alabama is labeled Leccinum rubropunctum, but is not cited or described in the 1971 publication, which designated Michigan as its study area. Snell's portion of the Boletus longicurvipes type collection (WHS 897, cited along with AHS 10320 in the original description) is now in BPI, labeled Leccinum rubropunctum, citing Snell himself as the determiner. Thus one of the two authors of Boletus longicurvipes (Smith) continued to believe it was distinct from Peck's Boletus rubropunctus; the other author (Snell) apparently agreed with Singer and others that the two were synonymous. Smith may never have seen rubropunctus in the fresh state; Snell probably did, but did not describe it separately--though the Dick illustration for Leccinum rubropunctum in Snell's monograph (Plate 62) appears to depict two rather distinct mushrooms, one of which has a bright yellow pore surface and a yellow stem (Leccinum rubropunctum?) and one of which has a dull yellowish pore surface and a whitish stem (Leccinum longicurvipes?). Smith and Thiers felt the two taxa were reliably separated by spore size, but they apparently based this claim on analysis of one Boletus rubropunctus specimen (the type), and unless the idea is supported by future analysis of many well documented specimens it should be discarded.

In this context of taxonomic and descriptive confusion, it should be clear that DNA results for "Leccinum rubropunctum" (Binder & Besl, 2000; Binder & Hibbett, 2004; den Bakker & Noordeloos, 2005) approach being meaningless. Four sequences bearing the species name Boletus rubropunctus are deposited in GenBank (AY612812, AY615911, AF139687, and AD001607) and have been aligned by these authors (clading with Leccinum longicurvipes and Leccinum subglabripes), but only two of the deposits cite a voucher, none cites a physical deposit in a public herbarium, and (most importantly) we have no idea who identified the specimens or what concept of "Boletus rubropunctus" was used.

The best way to clear up this mess would be to sequence the DNA of the type collections of the two taxa--but since that is unlikely (Peck's mushroom is 109 years old; Snell & Smith's mushrooms are 69 years old), Roy Halling's 2003 collection of Boletus rubropunctus (REH 8501) could serve as an initial representative for the taxon for further molecular and morphological studies.

The current European concept of Leccinum vulpinum (den Bakker & Noordeloos, 2005, 2006) is that of a conifer-associated, aurantiacum-like species with a dark reddish brown pileus, overhanging marginal flaps, black scabers, a bluing stipe base, faintly staining context, and generally clavate caulocystidia that are hyaline to brownish in KOH. According to den Bakker & Noordeloos (2005), "Leccinum vulpinum is probably common in North America" and is "commonly confused with L. aurantiacum."

Smith, Thiers & Watling (1966) describe a collection of Leccinum vulpinum from Barry County, Michigan (AHS 72725), "in mixed woods with pine," and this collection is again cited in Smith & Thiers (1971). Since Watling is the author of the species, he presumably agreed with the identification in the 1966 publication that bore his name and documented the Michigan collection--which means we can probably assume that this collection represents the concept of the species as it was named by Watling in 1961. I find no substantial differences between the Smith, Thiers & Watling description and the den Bakker & Noordeloos description.

No collections labeled Leccinum vulpinum are found in the online records of NY, TENN, BPI, or OSU. MICH holds 19 collections, 5 of which are Watling collections from conifer forests in Sweden, and 14 of which come from North America. Among the North American records that document tree associations (5 are silent on habitat) a few mention conifers but a small majority document hardwoods (primarily aspen). While misidentification resulting from the use of uninformative morphological characters may explain this discrepancy, it is also quite possible that conifers were in the collection areas and went unnoticed; most of the records in question come from woods I am quite familiar with (in Emmet and Cheboygan counties, in Michigan, and in San Miguel County, Colorado), and scattered conifers are almost always present in aspen-dominated stands in these areas.

Three partial sequences in GenBank bear the label Leccinum vulpinum. Two of these (AF454580, ITS1, 5.8S, ITS2, 28s; and AY538792, Gapdh) represent a den Bakker collection from Norway (hdb92). The third (AY538793, Gapdh) is a den Bakker collection from Canada (hdb415). The Norwegian collection is aligned in the papers of den Bakker and collaborators (2004a, 2004b), and the North American collection is cited in den Bakker & Noordeloos (2005) under "Collections studied" for Leccinum vulpinum, with a note saying its alignment "was nearly identical to the Gapdh sequence of L. vulpinum from Norway."

Leccinum ponderosum, from the Pacific Northwest and northern Rocky Mountains, is quite large (pileus 10-30 cm across), has an eagerly bluing stipe base, context that apparently does not stain gray, hymenial cystidia that are brown to ochraceous in KOH, and caulocystidia that are "smoky ochraceous" in KOH.